Plasminogen activator (PA) is a serine protease which exerts its action through hydrolysis of the Arg.sub.560 -Val.sub.561 peptide bond in plasminogen, yielding the 2-chain plasmin molecule. Plasmin has a general proteolytic activity and in the physiological environment of circulating blood it attacks mainly fibrin. Plasminogen activator plays a key role in the fibrinolytic system, which by lysing intra- or extra-vascular thrombi, clots, or fibrinous deposits, profoundly influences the incidence of thromboembolic vascular disease and its outcome.
Plasminogen activators have been isolated from body fluids such as blood and urine, and solid tissues of various histologic origin. Mammalian cell cultures are also known to produce plasminogen activators. There may be large differences in the amounts of plasminogen activator produced by cell lines derived from different tissues of the same animal, by cells of the same histologic type derived from cells of a single type independently transformed with the same oncogenic agent.
There is an urgent need for obtaining cells which are capable of producing increased amounts of PA and establishing techniques which would improve the process of using animal cell culture to produce PA on an industrial scale.